edu.emory.mathcs.backport.java.util
Class ArrayDeque

java.lang.Object
  java.util.AbstractCollection
      edu.emory.mathcs.backport.java.util.AbstractCollection
          edu.emory.mathcs.backport.java.util.ArrayDeque

All Implemented Interfaces:

java.lang.Cloneable, java.util.Collection, Deque, Queue, java.io.Serializable

public class ArrayDeque

extends AbstractCollection

implements Deque, java.lang.Cloneable, java.io.Serializable

Resizable-array implementation of the Deque interface. Array deques have no capacity restrictions; they grow as necessary to support usage. They are not thread-safe; in the absence of external synchronization, they do not support concurrent access by multiple threads. Null elements are prohibited. This class is likely to be faster than Stack when used as a stack, and faster than LinkedList when used as a queue.

Most ArrayDeque operations run in amortized constant time. Exceptions include remove, removeFirstOccurrence, removeLastOccurrence, contains, iterator.remove(), and the bulk operations, all of which run in linear time.

The iterators returned by this class's iterator method are fail-fast: If the deque is modified at any time after the iterator is created, in any way except through the iterator's own remove method, the iterator will generally throw a ConcurrentModificationException. Thus, in the face of concurrent modification, the iterator fails quickly and cleanly, rather than risking arbitrary, non-deterministic behavior at an undetermined time in the future.

Note that the fail-fast behavior of an iterator cannot be guaranteed as it is, generally speaking, impossible to make any hard guarantees in the presence of unsynchronized concurrent modification. Fail-fast iterators throw ConcurrentModificationException on a best-effort basis. Therefore, it would be wrong to write a program that depended on this exception for its correctness: the fail-fast behavior of iterators should be used only to detect bugs.

This class and its iterator implement all of the optional methods of the Collection and Iterator interfaces.

This class is a member of the Java Collections Framework.

Since:

1.6

Author:

Josh Bloch and Doug Lea

See Also:

Serialized Form

Constructor Summary

ArrayDeque()
Constructs an empty array deque with an initial capacity sufficient to hold 16 elements.

ArrayDeque(java.util.Collection c)
Constructs a deque containing the elements of the specified collection, in the order they are returned by the collection's iterator.

ArrayDeque(int numElements)
Constructs an empty array deque with an initial capacity sufficient to hold the specified number of elements.

Method Summary

boolean	add(java.lang.Object e) Inserts the specified element at the end of this deque.
void	addFirst(java.lang.Object e) Inserts the specified element at the front of this deque.
void	addLast(java.lang.Object e) Inserts the specified element at the end of this deque.
void	clear() Removes all of the elements from this deque.
java.lang.Object	clone() Returns a copy of this deque.
boolean	contains(java.lang.Object o) Returns true if this deque contains the specified element.
java.util.Iterator	descendingIterator() Returns an iterator over the elements in this deque in reverse sequential order.
java.lang.Object	element() Retrieves, but does not remove, the head of the queue represented by this deque.
java.lang.Object	getFirst() Retrieves, but does not remove, the first element of this deque.
java.lang.Object	getLast() Retrieves, but does not remove, the last element of this deque.
boolean	isEmpty() Returns true if this deque contains no elements.
java.util.Iterator	iterator() Returns an iterator over the elements in this deque.
boolean	offer(java.lang.Object e) Inserts the specified element at the end of this deque.
boolean	offerFirst(java.lang.Object e) Inserts the specified element at the front of this deque.
boolean	offerLast(java.lang.Object e) Inserts the specified element at the end of this deque.
java.lang.Object	peek() Retrieves, but does not remove, the head of the queue represented by this deque, or returns null if this deque is empty.
java.lang.Object	peekFirst() Retrieves, but does not remove, the first element of this deque, or returns null if this deque is empty.
java.lang.Object	peekLast() Retrieves, but does not remove, the last element of this deque, or returns null if this deque is empty.
java.lang.Object	poll() Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque), or returns null if this deque is empty.
java.lang.Object	pollFirst() Retrieves and removes the first element of this deque, or returns null if this deque is empty.
java.lang.Object	pollLast() Retrieves and removes the last element of this deque, or returns null if this deque is empty.
java.lang.Object	pop() Pops an element from the stack represented by this deque.
void	push(java.lang.Object e) Pushes an element onto the stack represented by this deque.
java.lang.Object	remove() Retrieves and removes the head of the queue represented by this deque.
boolean	remove(java.lang.Object o) Removes a single instance of the specified element from this deque.
java.lang.Object	removeFirst() Retrieves and removes the first element of this deque.
boolean	removeFirstOccurrence(java.lang.Object o) Removes the first occurrence of the specified element in this deque (when traversing the deque from head to tail).
java.lang.Object	removeLast() Retrieves and removes the last element of this deque.
boolean	removeLastOccurrence(java.lang.Object o) Removes the last occurrence of the specified element in this deque (when traversing the deque from head to tail).
int	size() Returns the number of elements in this deque.
java.lang.Object[]	toArray() Returns an array containing all of the elements in this deque in proper sequence (from first to last element).
java.lang.Object[]	toArray(java.lang.Object[] a) Returns an array containing all of the elements in this deque in proper sequence (from first to last element); the runtime type of the returned array is that of the specified array.

Methods inherited from class java.util.AbstractCollection

addAll, containsAll, removeAll, retainAll, toString

Methods inherited from class java.lang.Object

equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.Collection

addAll, containsAll, equals, hashCode, removeAll, retainAll

Constructor Detail

ArrayDeque

public ArrayDeque()

Constructs an empty array deque with an initial capacity sufficient to hold 16 elements.

ArrayDeque

public ArrayDeque(int numElements)

Constructs an empty array deque with an initial capacity sufficient to hold the specified number of elements.

Parameters:

numElements - lower bound on initial capacity of the deque

ArrayDeque

public ArrayDeque(java.util.Collection c)

Constructs a deque containing the elements of the specified collection, in the order they are returned by the collection's iterator. (The first element returned by the collection's iterator becomes the first element, or front of the deque.)

Parameters:

c - the collection whose elements are to be placed into the deque

Throws:

java.lang.NullPointerException - if the specified collection is null

Method Detail

addFirst

public void addFirst(java.lang.Object e)

Inserts the specified element at the front of this deque.

Specified by:

addFirst in interface Deque

Parameters:

e - the element to add

Throws:

java.lang.NullPointerException - if the specified element is null

addLast

public void addLast(java.lang.Object e)

Inserts the specified element at the end of this deque.

This method is equivalent to add(java.lang.Object).

Specified by:

addLast in interface Deque

Parameters:

e - the element to add

Throws:

java.lang.NullPointerException - if the specified element is null

offerFirst

public boolean offerFirst(java.lang.Object e)

Inserts the specified element at the front of this deque.

Specified by:

offerFirst in interface Deque

Parameters:

e - the element to add

Returns:

true (as specified by Deque.offerFirst(java.lang.Object))

Throws:

java.lang.NullPointerException - if the specified element is null

offerLast

public boolean offerLast(java.lang.Object e)

Inserts the specified element at the end of this deque.

Specified by:

offerLast in interface Deque

Parameters:

e - the element to add

Returns:

true (as specified by Deque.offerLast(java.lang.Object))

Throws:

java.lang.NullPointerException - if the specified element is null

removeFirst

public java.lang.Object removeFirst()

Description copied from interface: Deque

Retrieves and removes the first element of this deque. This method differs from pollFirst only in that it throws an exception if this deque is empty.

Specified by:

removeFirst in interface Deque

Returns:

the head of this deque

Throws:

java.util.NoSuchElementException

removeLast

public java.lang.Object removeLast()

Description copied from interface: Deque

Retrieves and removes the last element of this deque. This method differs from pollLast only in that it throws an exception if this deque is empty.

Specified by:

removeLast in interface Deque

Returns:

the tail of this deque

Throws:

java.util.NoSuchElementException

pollFirst

public java.lang.Object pollFirst()

Description copied from interface: Deque

Retrieves and removes the first element of this deque, or returns null if this deque is empty.

Specified by:

pollFirst in interface Deque

Returns:

the head of this deque, or null if this deque is empty

pollLast

public java.lang.Object pollLast()

Description copied from interface: Deque

Retrieves and removes the last element of this deque, or returns null if this deque is empty.

Specified by:

pollLast in interface Deque

Returns:

the tail of this deque, or null if this deque is empty

getFirst

public java.lang.Object getFirst()

Description copied from interface: Deque

Retrieves, but does not remove, the first element of this deque. This method differs from peekFirst only in that it throws an exception if this deque is empty.

Specified by:

getFirst in interface Deque

Returns:

the head of this deque

Throws:

java.util.NoSuchElementException

getLast

public java.lang.Object getLast()

Description copied from interface: Deque

Retrieves, but does not remove, the last element of this deque. This method differs from peekLast only in that it throws an exception if this deque is empty.

Specified by:

getLast in interface Deque

Returns:

the tail of this deque

Throws:

java.util.NoSuchElementException

peekFirst

public java.lang.Object peekFirst()

Description copied from interface: Deque

Retrieves, but does not remove, the first element of this deque, or returns null if this deque is empty.

Specified by:

peekFirst in interface Deque

Returns:

the head of this deque, or null if this deque is empty

peekLast

public java.lang.Object peekLast()

Description copied from interface: Deque

Retrieves, but does not remove, the last element of this deque, or returns null if this deque is empty.

Specified by:

peekLast in interface Deque

Returns:

the tail of this deque, or null if this deque is empty

removeFirstOccurrence

public boolean removeFirstOccurrence(java.lang.Object o)

Removes the first occurrence of the specified element in this deque (when traversing the deque from head to tail). If the deque does not contain the element, it is unchanged. More formally, removes the first element e such that o.equals(e) (if such an element exists). Returns true if this deque contained the specified element (or equivalently, if this deque changed as a result of the call).

Specified by:

removeFirstOccurrence in interface Deque

Parameters:

o - element to be removed from this deque, if present

Returns:

true if the deque contained the specified element

removeLastOccurrence

public boolean removeLastOccurrence(java.lang.Object o)

Removes the last occurrence of the specified element in this deque (when traversing the deque from head to tail). If the deque does not contain the element, it is unchanged. More formally, removes the last element e such that o.equals(e) (if such an element exists). Returns true if this deque contained the specified element (or equivalently, if this deque changed as a result of the call).

Specified by:

removeLastOccurrence in interface Deque

Parameters:

o - element to be removed from this deque, if present

Returns:

true if the deque contained the specified element

add

public boolean add(java.lang.Object e)

Inserts the specified element at the end of this deque.

This method is equivalent to addLast(java.lang.Object).

Specified by:

add in interface Deque

Parameters:

e - the element to add

Returns:

true (as specified by Collection.add(java.lang.Object))

Throws:

java.lang.NullPointerException - if the specified element is null

offer

public boolean offer(java.lang.Object e)

Inserts the specified element at the end of this deque.

This method is equivalent to offerLast(java.lang.Object).

Specified by:

offer in interface Deque

Parameters:

e - the element to add

Returns:

true (as specified by Queue.offer(java.lang.Object))

Throws:

java.lang.NullPointerException - if the specified element is null

remove

public java.lang.Object remove()

Retrieves and removes the head of the queue represented by this deque. This method differs from poll only in that it throws an exception if this deque is empty.

This method is equivalent to removeFirst().

Specified by:

remove in interface Deque

Returns:

the head of the queue represented by this deque

Throws:

java.util.NoSuchElementException

poll

public java.lang.Object poll()

Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque), or returns null if this deque is empty.

This method is equivalent to pollFirst().

Specified by:

poll in interface Deque

Returns:

the head of the queue represented by this deque, or null if this deque is empty

element

public java.lang.Object element()

Retrieves, but does not remove, the head of the queue represented by this deque. This method differs from peek only in that it throws an exception if this deque is empty.

This method is equivalent to getFirst().

Specified by:

element in interface Deque

Returns:

the head of the queue represented by this deque

Throws:

java.util.NoSuchElementException

peek

public java.lang.Object peek()

Retrieves, but does not remove, the head of the queue represented by this deque, or returns null if this deque is empty.

This method is equivalent to peekFirst().

Specified by:

peek in interface Deque

Returns:

the head of the queue represented by this deque, or null if this deque is empty

push

public void push(java.lang.Object e)

Pushes an element onto the stack represented by this deque. In other words, inserts the element at the front of this deque.

This method is equivalent to addFirst(java.lang.Object).

Specified by:

push in interface Deque

Parameters:

e - the element to push

Throws:

java.lang.NullPointerException - if the specified element is null

pop

public java.lang.Object pop()

Pops an element from the stack represented by this deque. In other words, removes and returns the first element of this deque.

This method is equivalent to removeFirst().

Specified by:

pop in interface Deque

Returns:

the element at the front of this deque (which is the top of the stack represented by this deque)

Throws:

java.util.NoSuchElementException

size

public int size()

Returns the number of elements in this deque.

Specified by:

size in interface Deque

Returns:

the number of elements in this deque

isEmpty

public boolean isEmpty()

Returns true if this deque contains no elements.

Specified by:

isEmpty in interface java.util.Collection

Returns:

true if this deque contains no elements

iterator

public java.util.Iterator iterator()

Returns an iterator over the elements in this deque. The elements will be ordered from first (head) to last (tail). This is the same order that elements would be dequeued (via successive calls to remove() or popped (via successive calls to pop()).

Specified by:

iterator in interface Deque

Returns:

an iterator over the elements in this deque

descendingIterator

public java.util.Iterator descendingIterator()

Description copied from interface: Deque

Returns an iterator over the elements in this deque in reverse sequential order. The elements will be returned in order from last (tail) to first (head).

Specified by:

descendingIterator in interface Deque

Returns:

an iterator over the elements in this deque in reverse sequence

contains

public boolean contains(java.lang.Object o)

Returns true if this deque contains the specified element. More formally, returns true if and only if this deque contains at least one element e such that o.equals(e).

Specified by:

contains in interface Deque

Parameters:

o - object to be checked for containment in this deque

Returns:

true if this deque contains the specified element

remove

public boolean remove(java.lang.Object o)

Removes a single instance of the specified element from this deque. If the deque does not contain the element, it is unchanged. More formally, removes the first element e such that o.equals(e) (if such an element exists). Returns true if this deque contained the specified element (or equivalently, if this deque changed as a result of the call).

This method is equivalent to removeFirstOccurrence(java.lang.Object).

Specified by:

remove in interface Deque

Parameters:

o - element to be removed from this deque, if present

Returns:

true if this deque contained the specified element

clear

public void clear()

Removes all of the elements from this deque. The deque will be empty after this call returns.

Specified by:

clear in interface java.util.Collection

toArray

public java.lang.Object[] toArray()

Returns an array containing all of the elements in this deque in proper sequence (from first to last element).

The returned array will be "safe" in that no references to it are maintained by this deque. (In other words, this method must allocate a new array). The caller is thus free to modify the returned array.

This method acts as bridge between array-based and collection-based APIs.

Specified by:

toArray in interface java.util.Collection

Overrides:

toArray in class AbstractCollection

Returns:

an array containing all of the elements in this deque

toArray

public java.lang.Object[] toArray(java.lang.Object[] a)

Returns an array containing all of the elements in this deque in proper sequence (from first to last element); the runtime type of the returned array is that of the specified array. If the deque fits in the specified array, it is returned therein. Otherwise, a new array is allocated with the runtime type of the specified array and the size of this deque.

If this deque fits in the specified array with room to spare (i.e., the array has more elements than this deque), the element in the array immediately following the end of the deque is set to null.

Like the toArray() method, this method acts as bridge between array-based and collection-based APIs. Further, this method allows precise control over the runtime type of the output array, and may, under certain circumstances, be used to save allocation costs.

Suppose x is a deque known to contain only strings. The following code can be used to dump the deque into a newly allocated array of String:

     String[] y = x.toArray(new String[0]);

Note that toArray(new Object[0]) is identical in function to toArray().

Specified by:

toArray in interface java.util.Collection

Overrides:

toArray in class AbstractCollection

Parameters:

a - the array into which the elements of the deque are to be stored, if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose

Returns:

an array containing all of the elements in this deque

Throws:

java.lang.ArrayStoreException - if the runtime type of the specified array is not a supertype of the runtime type of every element in this deque

java.lang.NullPointerException - if the specified array is null

clone

public java.lang.Object clone()

Returns a copy of this deque.

Returns:

a copy of this deque